The present invention is directed to EMT cell models and methods for their use in the identification of new anti-cancer agents for treating cancer patients, particularly in combination with other agents such as EGFR or IGF-1R kinase inhibitors that can be less effective at inhibiting tumor cells that have undergone an EMT. Cancer is a generic name for a wide range of cellular malignancies characterized by unregulated growth, lack of differentiation, and the ability to invade local tissues and metastasize. These neoplastic malignancies affect, with various degrees of prevalence, every tissue and organ in the body.
An anti-neoplastic drug would ideally kill cancer cells selectively, with a wide therapeutic index relative to its toxicity towards non-malignant cells. It would also retain its efficacy against malignant cells, even after prolonged exposure to the drug. Unfortunately, none of the current chemotherapies possess such an ideal profile. Instead, most possess very narrow therapeutic indexes. Furthermore, cancerous cells exposed to slightly sub-lethal concentrations of a chemotherapeutic agent will very often develop resistance to such an agent, and quite often cross-resistance to several other antineoplastic agents as well.
A multitude of therapeutic agents have been developed over the past few decades for the treatment of various types of cancer. The most commonly used types of anticancer agents include: DNA-alkylating agents (e.g., cyclophosphamide, ifosfamide), antimetabolites (e.g., methotrexate, a folate antagonist, and 5-fluorouracil, a pyrimidine antagonist), microtubule disrupters (e.g., vincristine, vinblastine, paclitaxel), DNA intercalators (e.g., doxorubicin, daunomycin, cisplatin), and hormone therapy (e.g., tamoxifen, flutamide). More recently, gene targeted therapies, such as protein-tyrosine kinase inhibitors have increasingly been used in cancer therapy (de Bono J. S. and Rowinsky, E. K. (2002) Trends in Mol. Medicine. 8:S19-S26; Dancey, J. and Sausville, E. A. (2003) Nature Rev. Drug Discovery 2:92-313). Such approaches, such as the EGFR kinase inhibitor erlotinib, are generally associated with reduced toxicity compared with conventional cytotoxic agents. They are therefore particularly appropriate for use in combination regimens. In pancreatic cancer, phase III trials have shown that first-line erlotinib treatment in combination with gemcitabine improves survival.
The epidermal growth factor receptor (EGFR) family comprises four closely related receptors (HER1/EGFR, HER2, HER3 and HER4) involved in cellular responses such as differentiation and proliferation. Over-expression of the EGFR kinase, or its ligand TGF-alpha, is frequently associated with many cancers, including breast, lung, colorectal, ovarian, renal cell, bladder, head and neck cancers, glioblastomas, and astrocytomas, and is believed to contribute to the malignant growth of these tumors. A specific deletion-mutation in the EGFR gene (EGFRvIII) has also been found to increase cellular tumorigenicity. Activation of EGFR stimulated signaling pathways promote multiple processes that are potentially cancer-promoting, e.g. proliferation, angiogenesis, cell motility and invasion, decreased apoptosis and induction of drug resistance. Increased HER1/EGFR expression is frequently linked to advanced disease, metastases and poor prognosis. For example, in NSCLC and gastric cancer, increased HER1/EGFR expression has been shown to correlate with a high metastatic rate, poor tumor differentiation and increased tumor proliferation.
Mutations which activate the receptor's intrinsic protein tyrosine kinase activity and/or increase downstream signaling have been observed in NSCLC and glioblastoma. However the role of mutations as a principle mechanism in conferring sensitivity to EGF receptor inhibitors, for example erlotinib (TARCEVA®) or gefitinib (IRESSA™), has been controversial. Recently, a mutant form of the full length EGF receptor has been reported to predict responsiveness to the EGF receptor tyrosine kinase inhibitor gefitinib (Paez, J. G. et al. (2004) Science 304:1497-1500; Lynch, T. J. et al. (2004) N. Engl. J. Med. 350:2129-2139). Cell culture studies have shown that cell lines which express the mutant form of the EGF receptor (i.e. H3255) were more sensitive to growth inhibition by the EGF receptor tyrosine kinase inhibitor gefitinib, and that much higher concentrations of gefitinib was required to inhibit the tumor cell lines expressing wild type EGF receptor. These observations suggests that specific mutant forms of the EGF receptor may reflect a greater sensitivity to EGF receptor inhibitors, but do not identify a completely non-responsive phenotype.
Erlotinib (e.g. erlotinib HCl, also known as TARCEVA® or OSI-774) is an orally available inhibitor of EGFR kinase. In vitro, erlotinib has demonstrated substantial inhibitory activity against EGFR kinase in many human tumor cell lines. In a phase III trial, erlotinib monotherapy significantly prolonged survival, delayed disease progression and delayed worsening of lung cancer-related symptoms in patients with advanced, treatment-refractory NSCLC (Shepherd, F. et al. (2005) N. Engl. J. Med. 353(2):123-132). In November 2004 the U.S. Food and Drug Administration (FDA) approved TARCEVA® for the treatment of patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) after failure of at least one prior chemotherapy regimen.
The development for use as anti-tumor agents of compounds that directly inhibit the kinase activity of IGF-1R, as well as antibodies that reduce IGF-1R kinase activity by blocking IGF-1R activation or antisense oligonucleotides that block IGF-1R expression, are also areas of intense research effort (e.g. see Larsson, O. et al (2005) Brit. J. Cancer 92:2097-2101; Ibrahim, Y. H. and Yee, D. (2005) Clin. Cancer Res. 11:944s-950s; Mitsiades, C. S. et al. (2004) Cancer Cell 5:221-230; Camirand, A. et al. (2005) Breast Cancer Research 7:R570-R579 (DOI 10.1186/bcr1028); Camirand, A. and Pollak, M. (2004) Brit. J. Cancer 90:1825-1829; Garcia-Echeverria, C. et al. (2004) Cancer Cell 5:231-239).
IGF-1R is a transmembrane RTK that binds primarily to IGF-1 but also to IGF-II and insulin with lower affinity. Binding of IGF-1 to its receptor results in receptor oligomerization, activation of tyrosine kinase, intermolecular receptor autophosphorylation and phosphorylation of cellular substrates (major substrates are IRS1 and Shc). The ligand-activated IGF-1R induces mitogenic activity in normal cells and plays an important role in abnormal growth. A major physiological role of the IGF-1 system is the promotion of normal growth and regeneration. Overexpressed IGF-1R (type 1 insulin-like growth factor receptor) can initiate mitogenesis and promote ligand-dependent neoplastic transformation. Furthermore, IGF-1R plays an important role in the establishment and maintenance of the malignant phenotype. Unlike the epidermal growth factor (EGF) receptor, no mutant oncogenic forms of the IGF-1R have been identified. However, several oncogenes have been demonstrated to affect IGF-1 and IGF-1R expression. The correlation between a reduction of IGF-1R expression and resistance to transformation has been seen. Exposure of cells to the mRNA antisense to IGF-1R RNA prevents soft agar growth of several human tumor cell lines. IGF-1R abrogates progression into apoptosis, both in vivo and in vitro. It has also been shown that a decrease in the level of IGF-1R below wild-type levels causes apoptosis of tumor cells in vivo. The ability of IGF-1R disruption to cause apoptosis appears to be diminished in normal, non-tumorigenic cells.
The IGF-1 pathway in human tumor development has an important role. IGF-1R overexpression is frequently found in various tumors (breast, colon, lung, sarcoma) and is often associated with an aggressive phenotype. High circulating IGF1 concentrations are strongly correlated with prostate, lung and breast cancer risk. Furthermore, IGF-1R is required for establishment and maintenance of the transformed phenotype in vitro and in vivo (Baserga R. Exp. Cell. Res., 1999, 253, 1-6). The kinase activity of IGF-1R is essential for the transforming activity of several oncogenes: EGFR, PDGFR, SV40 T antigen, activated Ras, Raf, and v-Src. The expression of IGF-1R in normal fibroblasts induces neoplastic phenotypes, which can then form tumors in vivo. IGF-1R expression plays an important role in anchorage-independent growth. IGF-1R has also been shown to protect cells from chemotherapy-, radiation-, and cytokine-induced apoptosis. Conversely, inhibition of endogenous IGF-1R by dominant negative IGF-1R, triple helix formation or antisense expression vector has been shown to repress transforming activity in vitro and tumor growth in animal models.
During most cancer metastases, an important change occurs in a tumor cell known as the epithelial-mesenchymal transition (EMT) (Thiery, J. P. (2002) Nat. Rev. Cancer 2:442-454; Savagner, P. (2001) Bioessays 23:912-923; Kang Y. and Massague, J. (2004) Cell 118:277-279; Julien-Grille, S., et al. Cancer Research 63:2172-2178; Bates, R. C. et al. (2003) Current Biology 13:1721-1727; Lu Z., et al. (2003) Cancer Cell. 4(6):499-515)). EMT does not occur in healthy cells except during embryogenesis. Epithelial cells, which are bound together tightly and exhibit polarity, give rise to mesenchymal cells, which are held together more loosely, exhibit a loss of polarity, and have the ability to travel. These mesenchymal cells can spread into tissues surrounding the original tumor, as well as separate from the tumor, invade blood and lymph vessels, and travel to new locations where they divide and form additional tumors. Recent research has demonstrated that epithelial cells respond well to EGFR and IGF-1R kinase inhibitors, but that after an EMT the resulting mesenchymal-like cells are much less sensitive to such inhibitors. (e.g. Thompson, S. et al. (2005) Cancer Res. 65(20):9455-9462; U.S. Patent Application 60/997,514). Thus there is a pressing need for anti-cancer agents that can prevent or reverse tumor cell EMT events (e.g. stimulate a mesenchymal to epithelial transition (MET)), or inhibit the growth of the mesenchymal-like tumor cells resulting from EMT. Such agents should be particularly useful when used in conjunction with other anti-cancer drugs such as EGFR and IGF-1R kinase inhibitors.
As human cancers progress to a more invasive, metastatic state, multiple signaling programs regulating cell survival and migration programs are observed depending on cell and tissue contexts (Gupta, G. P., and Massague, J. (2006) Cell 127, 679-695). Recent data highlight the transdifferentiation of epithelial cancer cells to a more mesenchymal-like state, a process resembling epithelial-mesenchymal transition (EMT; (Oft, M., et al. (1996). Genes & development 10, 2462-2477; Perl, A. K., et al. (1998). Nature 392, 190-193), to facilitate cell invasion and metastasis (Brabletz, T. et al. (2005) Nat Rev Cancer 5, 744-749; Christofori, G. (2006) Nature 441, 444-450). Through EMT-like transitions mesenchymal-like tumor cells are thought to gain migratory capacity at the expense of proliferative potential. A mesenchymal-epithelial transition (MET) has been postulated to regenerate a more proliferative state and allow macrometastases resembling the primary tumor to form at distant sites (Thiery, J. P. (2002) Nat Rev Cancer 2, 442-454). EMT-like transitions in tumor cells result from transcriptional reprogramming over considerable periods of time (weeks to months) via transcription factors harboring zinc finger, forkhead, bHLH and HMG-box domains (Mani, S. A. et al. (2007) Proceedings of the National Academy of Sciences of the United States of America 104, 10069-10074; Peinado, H. et al. (2007) Nat Rev Cancer 7, 415-428). The loss of E-cadherin and transition to a more mesenchymal-like state likely serves a major role in the progression of cancer (Matsumura, T. et al. (2001) Clin Cancer Res 7, 594-599; Yoshiura, K. et al. (1995). Proceedings of the National Academy of Sciences of the United States of America 92, 7416-7419) and the acquisition of a mesenchymal phenotype has been correlated with poor prognosis (Baumgart, E. et al. (2007) Clin Cancer Res 13, 1685-1694; Kokkinos, M. I. Et al. (2007) Cells, tissues, organs 185, 191-203; Willipinski-Stapelfeldt, B. et al. (2005) Clin Cancer Res 11, 8006-8014.). Targeting tumor-derived and/or tumor-associated stromal cells provides a unique mechanism to block EMT-like transitions and inhibit the survival of invading cells.
The cellular changes associated with EMT-like transitions alter the dependence of carcinoma cells on EGF receptor signaling networks for survival. It has been observed that an EMT-like transition was associated with cellular insensitivity to the EGFR-TKI erlotinib (Thomson, S. et al. (2005) Cancer research 65, 9455-9462; Witta, S. E., et al. (2006) Cancer research 66, 944-950; Yauch, R. L., et al. (2005) Clin Cancer Res 11, 8686-8698), in part from EGFR independent activation of either or both the PI3′ kinase or Mek-Erk pathways (Buck, E. et al. (2007). Molecular cancer therapeutics 6, 532-541). Similar data correlating EMT status to sensitivity to EGFR TKIs have been reported in pancreatic, CRC (Buck, E. et al. (2007) Molecular cancer therapeutics 6, 532-541) bladder (Shrader, M. et al. (2007) Molecular cancer therapeutics 6, 277-285) and HNSCC (Frederick et al. (2007) Molecular cancer therapeutics 6, 1683-1691) cell lines, xenografts and in patients (Yauch, R. L., et al. (2005) Clin Cancer Res 11, 8686-8698). The molecular determinants to alternative routes of activation of the PI3′ kinase and Erk pathways, which can bypass cellular sensitivity to EGF receptor inhibitors, have been actively investigated (Chakravarti, A. et al. (2002) Cancer research 62, 200-207; Engelman, J. A. et al. (2007) Science 316:1039-1043).
Inhibition of EMT-like transitions and mesenchymal-like cell survival would be predicted to reduce tumor metastasis and progression. Current data suggest patients with metastasis have heterogeneous tumors that can contain cells with epithelial and mesenchymal-like phenotypes. The observation that tumors can acquire new signaling pathways, for example PDGFR and FGFR autocrine signaling, suggest new therapeutic modalities to target specific tumor cell populations. These data suggest rational drug combinations that would not only cause growth inhibition or apoptosis of tumor cells directly, but would also impact mesenchymal cell populations promoting cancer recurrence (Moody, S. E. et al. (2005). Cancer cell 8, 197-209). Essential for the discovery and development of such drug combinations will be the availability of good cellular and animal models where their efficacy can be readily assessed. The invention described herein provides such models.